Method and system for switching a radio access technology between wireless communication systems with a multi-mode wireless transmit/receive unit

ABSTRACT

A method and system for switching a radio access technology (RAT) between wireless communication systems connected to each other while implementing different RATs with a multi-mode WTRU are disclosed. A plurality of wireless communication systems are deployed with overlapping coverage areas wherein each system implements different RATs and are connected to each other such that a service that is provided by one system may be provided through the other system. Each wireless communication system transmits an indication of the existence of an inter-working wireless communication system in a coverage area of each system. The WTRU receives the indication and information regarding the inter-working wireless communication system. The WTRU then initiates a handoff to the inter-working wireless communication system using the received information, whereby the WTRU continues to receive the same services that the WTRU receives from the currently connected wireless communication system through the inter-working wireless communication system.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No. 60/552,561 filed Mar. 12, 2004, which is incorporated by reference as if fully set forth.

FIELD OF INVENTION

The present invention is related to a wireless communication system. More particularly, the present invention is a method and system for switching a radio access technology (RAT) between wireless communication systems being connected to each other while implementing different RATs with a multi-mode wireless transmit/receive unit (WTRU).

BACKGROUND

Universal mobile telecommunication systems (UMTS) and wireless local area network (WLAN) technologies are widely used in current wireless communication systems. Since the coverage areas of UMTS and WLANs are often overlapped, an inter-networking of UMTS and WLAN networks has been developed. An inter-working WLAN (I-WLAN) is a WLAN with a connection to a UMTS core network so that the services provided by the UMTS may be forwarded through the I-WLAN.

Currently, the network selection of an I-WLAN requires that a WTRU scan for available WLAN systems using their service set identifiers (SSIDs). The scanning of SSIDs can be done either passively or actively. In passive scanning, the WTRU observes information broadcast from each WLAN and determines its availability according to the signal strength. In active scanning, the WTRU transmits a probe request containing a specific WLAN SSID and waits for confirmation of the availability from that WLAN.

These techniques, however, do not provide any indication of the WLAN (SSID) that provides access to UMTS based services. Several solutions have been devised including broadcasting of the home public land mobile network (PLMN) identification over the WLAN broadcast channel. However, such techniques are vulnerable to spoofing, (disruptive WLAN operators may broadcast the same SSIDs and PLMN ID), since WLAN SSIDs are not unique.

Therefore, the selection of a UMTS based I-WLAN for connecting to UMTS based services can be a problem due to the large number of WLAN networks (SSIDs) that the WTRU must choose from and the ease of using similar SSIDs by disruptive operators in order to direct the traffic toward their networks. Accordingly, there is a need for a method and system for providing an indication of WLANs (SSIDs) that provide access to UMTS based services.

SUMMARY

The present invention is a method and system for switching a radio access technology (RAT) between wireless communication systems connected to each other while implementing different RATs with a multi-mode WTRU. A plurality of wireless communication systems are deployed with overlapping coverage areas wherein each wireless communication system implements different RATs and are connected to each other such that a service that is provided by one wireless communication system may be provided through the other wireless communication system. Each wireless communication system transmits an indication of the existence of an inter-working wireless communication system in a coverage area of each wireless communication system. The WTRU receives the indication and information regarding the inter-working wireless communication system. The WTRU then initiates a handoff to the inter-working wireless communication system using the received information, whereby the WTRU continues to receive the same services that the WTRU receives from the currently connected wireless communication system through the inter-working wireless communication system. The present invention helps reduce the time taken by the multi-mode WTRU to select and authenticate the inter-working wireless communication system.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding of the invention may be had from the following description of a preferred embodiment, given by way of example and to be understood in conjunction with the accompanying drawing wherein:

FIG. 1 is a block diagram of a wireless communication system in accordance with the present invention;

FIG. 2 is a flow diagram of a process for switching a radio access technology (RAT) in accordance with the present invention; and

FIG. 3 is a signaling diagram of a process for exchanging messages among a WTRU, a UMTS terrestrial radio access network (UTRAN), and a WLAN for handoff from the UTRAN to the WLAN in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereafter, the terminology “WTRU” includes but is not limited to a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referred to hereafter, the terminologies “base station” and “access point (AP)” include but are not limited to a Node-B, a site controller or any other type of interfacing device in a wireless environment.

FIG. 1 is a block diagram of a wireless communication system 100 in accordance with the present invention. The system 100 comprises at least two different types of wireless communication networks 110, 120 implementing different radio access technologies (RATs). For example, as shown in FIG. 1, one type of wireless network is a UMTS terrestrial radio access network (UTRAN) (see UTRAN cell 110) preferably operating under third generation partnership project (3GPP) standards and the other type of wireless network is a WLAN 120 preferably operating under IEEE 802.11 standards. For purposes of describing the present invention, only one UTRAN cell 110 is shown. However, it is noted that, a UTRAN typically includes a plurality of cells, as known to those skilled in the art.

For convenience, the present invention is described with reference to a UTRAN and a WLAN. However, it should be noted that it is obvious to those skilled in the art that the present invention may be applied to any type of wireless communication system and further that there could be more than two different types of wireless communication networks.

Coverage areas of the wireless communication systems 110, 120 are overlapping with respect to each other. In a UTRAN-WLAN example, as is used herein, the coverage area of the WLAN 120 typically falls within the larger coverage area of a UTRAN cell 110. The WLAN 120 is connected to the UTRAN cell 110 so that the services provided within the UTRAN cell 110 may be forwarded to a multi-mode WTRU 102 through the WLAN 120. The WLAN 120 may therefore also be referred to as an I-WLAN, as explained above. A multi-mode WTRU 102 located in the overlapping area may access both types of wireless communication networks simultaneously, and may receive services provided by one network through the other network.

In accordance with the present invention, the UTRAN cell 110 sends an indication of the existence of any I-WLANs, or alternatively a list of service set identifiers (SSIDs) of the I-WLANs, located in the UTRAN cell 110 to the WTRU 102. The indication or the list of SSIDs may be transmitted as desired. For example, they may be broadcast via a broadcast control channel (BCCH) or may be sent via a dedicated control channel (DCCH). Where a system 100 is configured to transmit the indication or list over BCCHs, WTRUs may, but are not required to, provide their WLAN capability (i.e. whether or not they are capable of operating in a WLAN) upon connecting to the UTRAN cell 110 or upon establishment of a radio bearer. Where a system 100 is configured to transmit the indication or list over DCCHs, WTRUs are preferably required to provide their WLAN capability upon connecting to the UTRAN cell 110 or upon establishment of a radio bearer.

In accordance with a first embodiment, only an indication of the existence of any I-WLANs within the UTRAN cell 110 is transmitted. As mentioned above, the indication may be transmitted as desired, but is preferably transmitted over the cell's 110 broadcast control channel (BCCH) or over a dedicated control channel (DCCH). The WTRU 102 receives the indication and if a predetermined criteria for inter-system handoff (i.e. a predetermined criteria for handing over a WTRU 102 from the UTRAN cell 110 to the WLAN 120) is satisfied, the WTRU 102 requests the list of SSIDs from the UTRAN cell 110. It should be noted, of course, that the predetermined criteria may be any type of criteria and the evaluation of whether to actually perform an inter-system handoff may be evaluated by the WTRU 102 or by any of the network components of the network from which a handoff may occur, which in this case is a UTRAN.

Once the WTRU 102 receives the SSID list, the SSIDs are used, passively or actively, for scanning, association, and authentication of an appropriate AP within the I-WLAN 120. This scheme ensures that the WTRU 102 accesses the right WLAN AP that provides a connection to the UTRAN cell 110 and its 3GPP based services. Where the inter-system handoff criteria is met and there is an appropriate AP within the I-WLAN 120 to handoff to, the WTRU 102 is handed-off to the I-WLAN 120 and begins operating therein.

As an alternative, the WTRU 102 may request the list of SSIDs prior to evaluation of the inter-system handoff criteria in order to confirm whether there is an appropriate AP available prior to performing the evaluation.

In accordance with a second embodiment, the system 100 operates as mentioned above, but in this embodiment instead of first transmitting an indication of the existence of any I-WLANs within the UTRAN cell 110, the UTRAN cell 110 simply transmits the list of SSIDs. This may provide enhance performance where the number of SSIDs is not too high. Whether to implement the first or second embodiment is operator preference.

FIG. 2 is a flow diagram of a process 200 for switching a RAT in accordance with the present invention. A plurality of wireless communication systems are deployed with overlapping coverage areas. Each wireless communication system implements a different RAT and are configured such that a service that is provided by one wireless communication system may be provided through the other wireless communication system.

Each wireless communication system transmits an indication of the existence of an inter-working wireless communication system, optionally along with information of the alternative wireless communication system (including an identifier, frequency, etc), which implements a different RAT within the coverage area of each wireless communication system (step 202). The indication and/or the information may be broadcast to WTRUs or may be sent via a dedicated channel for the WTRUs. The WTRU receives the indication and/or the information through a currently connected wireless communication system (i.e. the wireless communication system to which the WTRU is currently connected) (step 204).

Alternatively, the indication and/or the information may be transmitted in response to a request message for the information or a capability report from the WTRU. In response, the currently connected wireless communication system sends an indication of availability of the inter-working wireless communication system and/or the information about the inter-working wireless communication system to the WTRU. In such case, the indication and/or the information may be transmitted via a DCCH to the WTRU.

After receiving the indication and/or the information, it is determined whether to initiate a handoff to the inter-working wireless communication system (step 206). As mentioned above, this determination may be made at the network or at the WTRU and may be based on any predetermined criteria, as desired. The handoff may be initiated by a user's request or may be initiated autonomously based on service requirements. The WTRU may display the availability of the inter-working wireless communication system on its display screen or provide an alarm alerting the user of the same. If it is determined to handoff the WTRU to the inter-working wireless communication system and if only the indication has been sent, the WTRU requests the information regarding the inter-working wireless communication system and receives it from the currently connected wireless communication system (step 208). If the information has been transmitted along with the indication or is simply sent without any indication, step 208 is skipped. The WTRU then initiates a handoff procedure using the received information (step 210).

In the context of a UTRAN-WLAN example as used herein, the information may be SSIDs of the I-WLANs, and optionally may further include a corresponding PLMN ID and the corresponding coordinates, (i.e., location), of each SSID. The WTRU initiates active or passive scanning for the identified WLANs after receiving the SSIDs of the I-WLANs. The WLAN scanning may be limited to WLANs identified by the received SSIDs.

Association with a particular WLAN AP may be based on channel quality measurements. If channel quality measurements from all WLANs are under a predefined threshold, the initial UTRAN connection is maintained. If an acceptable WLAN AP is found, the UTRAN may be notified of the cell change over the DCCH of the cell change. Connection security may be enabled by information such as wired equivalent privacy (WEP) information. The WTRU continues to scan for APs of common SSIDs of WLAN association and disassociation procedures. If an acceptable AP is not found, the WTRU may either scan for an alternate WLAN identified by a known SSID, or revert back to the UTRAN connection. In this case, an inter RAT cell change indication may be signaled. The choice to switch RATs may either be autonomous based on quality measurements within a predefined threshold or manually controlled by user input. After the RAT cell change, the WTRU continues to receive the same services that the WTRU receives from the currently connected wireless communication system through the alternative wireless communication system.

FIG. 3 is a signaling diagram of an exemplary process 300 for exchanging messages among a WTRU 102, a UTRAN cell 110, and a WLAN 120 for handoff from the UTRAN cell 110 to the WLAN 120 in accordance with the present invention. The UTRAN cell 110 transmits an indication of availability of any I-WLANs, (and/or optionally along with a list of SSIDs of available WLANs) (step 302). The transmission may be triggered by a report from the WTRU 102 indicating WLAN capability of the WTRU 102. The WTRU 102 receives the I-WLAN availability indication and/or list of SSIDs (step 304). In the case that only the indication is transmitted, the WTRU 102 sends a request for SSIDs of WLANs (step 306). In the case that the SSID list is transmitted along with the indication or the list is sent without any indication, steps 306-310 are omitted. Upon receipt of the request, the UTRAN cell 110 retrieves the SSIDs information (step 308). The UTRAN cell 110 transmits the list of WLAN SSIDs and optionally their associated locations and PLMN ID (step 310). After receiving the list of SSIDs, the WTRU 102 stores them in a memory and scans, either actively or passively, for an appropriate AP using the list (step 312). If the WTRU 102 is within the range of the WLAN coverage, the WTRU 102 initiates an I-WLAN selection (step 312). The WTRU 102 initiates a WLAN service with the selected WLAN (step 314). The WLAN 120 authenticates the WTRU 102 and may allocate a new IP address, if necessary, which typically depends on the type of inter-working scheme being implemented, as explained in more detail below (step 316). After authentication is completed at step 318, access to the WLAN service is granted for the WTRU 102 (step 320).

As mentioned above, different inter-working schemes may be used for connecting the I-WLAN to the UTRAN. For example, under the current wireless communication standards, the I-WLAN may be connected to the 3GPP system via a core network, (i.e., packet date gateway (PDG)), or via the UTRAN as a pipe. In the latter case, no new IP address is assigned in case of I-WLAN reselection, (handoff from the 3GPP system to I-WLAN). In the former case, (i.e., PDG based interworking), new procedures are used to allocate an IP address to the WTRU operating in the I-WLAN. These procedures are different than those used in the 3GPP system and thus may result in the assignment of a new IP address for the WTRU.

Although the elements in the Figures are illustrated as separate elements, these elements may be implemented on a single integrated circuit (IC), such as an application specific integrated circuit (ASIC), multiple ICs, discrete components, or a combination of discrete components and IC(s). Although the features and elements of the present invention are described in the preferred embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention. Furthermore, the present invention may be implemented in any type of wireless communication system. 

1. A method implemented in a multi-mode wireless transmit/receive unit (WTRU), the method comprising: receiving a service from a core network via a cellular access network; sending a first message via the cellular access network, the first message indicating that the WTRU is capable of communicating using wireless local area network (WLAN) technology; receiving a second message via the cellular access network, wherein the second message is responsive to the first message and includes Service Set Identifiers (SSIDs) indicating WLANs available for handoff; selecting one of the WLANs indicated by the SSIDs; initiating a handover to the selected WLAN; and in response to the handover, receiving the service from the core network via the selected WLAN.
 2. The method of claim 1 wherein the second message includes location information for the WLANs indicated by the SSIDs.
 3. The method of claim 1, further comprising: scanning for the WLANs indicated by the SSIDs.
 4. The method of claim 3 wherein the selecting one of the WLANs is based on a channel quality measurement.
 5. The method of claim 1 wherein the selecting one of the WLANs is based on input from a user of the WTRU.
 6. The method of claim 1 wherein the selecting one of the WLANs is based on requirements of the service.
 7. The method of claim 1 wherein the receiving the service via the selected WLAN includes receiving the service via a packet data gateway (PDG).
 8. The method of claim 1 wherein the cellular access network is based on Third Generation Partnership Project (3GPP) technology.
 9. A wireless transmit/receive unit (WTRU) comprising: a transmitter configured to send a first message via a cellular access network, the first message indicating that the WTRU is capable of communicating using wireless local area network (WLAN) technology; a receiver configured: to receive a service from a core network via the cellular access network; and to receive a second message via the cellular access network, wherein the second message is responsive to the first message and includes Service Set Identifiers (SSIDs) of WLANs available for handoff; and a processor configured to select one of the WLANs indicated by the SSIDs and to initiate a handover to the selected WLAN; wherein the receiver is configured to receive the service via the selected WLAN in response to the handover.
 10. The WTRU of claim 9 wherein the second message includes location information for the WLANs indicated by the SSIDs.
 11. The WTRU of claim 9 wherein the receiver is further configured to scan for the WLANs indicated by the SSIDs.
 12. The WTRU of claim 11 wherein the processor is configured to select one of the WLANs indicated by the SSIDs based on a channel quality measurement.
 13. The WTRU of claim 9 wherein the processor is configured to select one of the WLANs based on input from a user of the WTRU.
 14. The WTRU of claim 9 wherein the processor is configured to select one of the WLANs based on requirements of the service.
 15. The WTRU of claim 9 wherein the receiver is configured to the receive the service via the selected WLAN via a packet data gateway (PDG).
 16. The WTRU of claim 9 wherein the cellular access network is based on Third Generation Partnership Project (3GPP) technology.
 17. A method for use in a wireless transmit/receive unit (WTRU), the method comprising: receiving a service from a core network via a cellular access network; sending a first message via the cellular access network, the first message indicating that the WTRU is capable of communicating using wireless local area network (WLAN) technology; receiving a second message via the cellular access network that is responsive to the first message, the second message including Service Set Identifiers (SSIDs) indicating WLANs available for handoff; selecting one of the WLANs indicated by the SSIDs; initiating a handover to the selected WLAN; and upon completion of the handover, receiving the service from the core network via the selected WLAN.
 18. A wireless transmit/receive unit (WTRU) comprising: a transmitter configured to send a first message via a cellular access network, the first message indicating that the WTRU is capable of communicating using wireless local area network (WLAN) technology; a receiver configured: to receive a service from a core network via the cellular access network; and to receive a second message via the cellular access network, wherein the second message is responsive to the first message and includes Service Set Identifiers (SSIDs) of WLANs available for handoff; and a processor configured to select one of the WLANs indicated by the SSIDs and to initiate a handover to the selected WLAN; wherein the receiver is configured to receive the service via the selected WLAN upon completion of the handover. 